Everything You’ve Always Wanted to Know About Egg Allergy

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Egg is a well-known trigger of childhood allergy, typically affecting more children than any other food besides milk. However, it affects a surprisingly large number of adults, too. Although children are more likely to react to egg after eating it, adults are more likely to react to egg after some time spent in an egg-related job, such as breeding birds or baking bread. Symptoms of egg allergy range from mild to severe and can occur within a few minutes to a few days after eating egg-containing food. Some people also react to certain egg-containing medications like certain over-the-counter cold medicines and the yellow fever vaccine. Oral immunotherapy offers a long-term solution for people with persistent egg allergies, but many of those who cannot benefit from that type of treatment can still enjoy baked goods.

And now for the details, which include:

What is an allergy to egg?

Chickens were domesticated for their eggs over 5000 years ago from the Red Jungle Fowl (species Gallus gallus) that was native to southern Asia and can still be found in India, China, Malaysia, Indonesia, Java and the Philippines. The chicken currently used for both meat and egg production is the sub-species Gallus gallus domesticus.

The breeds currently dominating the world’s poultry industry were all produced using selective breeding techniques during the ‘hen craze’ of the nineteenth century and come primarily from:

• the Cornish—the foundation of our modern broiler industry
• the White Leghorn—the producer of industrial white-shelled eggs (brown-shelled eggs are produced from crosses of several dual purpose breeds)
• the Plymouth Rock—a dual-purpose breed

Meanwhile, the original Red Jungle Fowl is now endangered, partly through loss of habitat and partly because it breeds easily with its domesticated offspring, yielding a hybrid bird and thus diluting its bloodline. Some people keep Red Jungle Fowl in captivity to help preserve them and there is even a studbook for the species, with many breeders having their birds’ DNA tested for species purity.

Eggs are eaten all over the world, either raw, slightly cooked (poached, soft-boiled or scrambled) or well-done (fried, hard-boiled or well baked). They’re also an important ingredient in a large number of other foods, ranging from bread and pasta to salad dressing, confectionery and ice cream, where they act as colourants, clarifiers, emulsifiers, binders, coagulants and nutrition supplementing agents, as well as adding shine to baked goods. The antibacterial properties of some of the components of egg white make it a valuable raw material in the cosmetic and pharmaceutical industries.

Most of the eggs we eat In Europe, Australasia and the US come from chickens, but in parts of Europe and Asia, duck, quail and goose eggs are also commonly consumed.

Eggs are widely used because they are cheap, versatile and very nutritious (and not bad for your cholesterol levels, in case you wondered). Egg is a rich source of fats, vitamins and minerals and, notably, proteins, which make up about 12.5g/100g (12.5%) of the whole egg.

Unfortunately, egg can cause allergic reactions in a small percentage people. This happens because their body’s immune system mistakes one or more harmless egg proteins for toxic invaders and creates IgE antibodies against them. The next time they eat egg, these antibodies recognise the proteins and prompt a response from immune system cells. These, in turn, release a variety of chemicals into the bloodstream, including histamine, the chemical that is primarily responsible for the symptoms of allergy.

The first documented description of ‘egg poisoning’ was given in 1908 by London doctor Alfred T. Schofield who published a case report involving a 13-year-old boy in the medical journal the Lancet.

The first documented report of a food allergy diagnosis also involves egg allergy. It was given in 1912 by American paediatrician Oscar Menderson Schloss, who diagnosed a 14-month-old boy who developed hives and facial swelling immediately after ingesting egg using what was probably the first skin scratch test.

A person can be allergic to one or more proteins in the yolk and/or the egg white. Someone with an allergy to proteins in the yolk may be able to tolerate the white of the egg, and vice versa.

Because most of the proteins that trigger egg allergy are found in the whites of the egg, allergy to egg whites is more common. Additionally, the proteins in the egg white tend to be more resistant to cooking and digestion and are therefore regarded as more allergenic. As such, egg white is often used in lab tests when trying to diagnose a person with a suspected egg allergy.

In fact, until recently, an allergy to egg yolk was not thought to be possible without a concurrent allergy to egg white. We now know that a person can become allergic to egg yolk due to bird-egg syndrome, where a sensitisation to bird proteins (in feathers and droppings) causes cross-reactivity to egg yolk. Egg yolk allergy predominantly affects adults, while egg white allergy often affects children.

Symptoms of egg allergy are varied and wide-ranging. Eggs can cause IgE-mediated reactions (the ‘classic’ type of allergy) as well as non-IgE-mediated reactions and mixed IgE- and non-IgE-mediated reactions.

Non IgE-mediated diseases include food protein-induced allergic proctocolitis (FPIAP), food protein-induced enteropathy (FPE) and food protein–induced enterocolitis syndrome (FPIES), and mixed diseases include atopic dermatitis, eosinophilic gastroenteritis (EGE) and eosinophilic oesophagitis (EoE). These diseases can be triggered by either egg yolk and/or egg white and affect both children and adults.

Atopic dermatitis (AD), aka allergic eczema, which I shall just call ‘eczema’ (although, strictly-speaking, AD is the most common subtype of eczema), can be provoked and exacerbated by eating egg. It can either be an IgE-mediated form of allergy and produce symptoms soon after eating the offending food, or it can be a non-IgE-mediated form and show up several hours or days later. The IgE-mediated form is more common in childhood.

Food allergies are on the rise and this is thought to be, in large part, because of the widely increasing numbers of children with egg allergy. The number of serious allergic reactions to egg may also be on the rise.

Identified allergens

The proteins (and occasionally carbohydrates) in a food that are capable of provoking allergic reactions are called allergens. Allergens are named using the first three letters of the genus—Gallus—the first letter of the species—domesticus—and a number generally reflecting the order in which they were identified.

As of March 2026, 6 chicken egg allergens have been added to the WHO/IUIS allergen database (the official, peer-reviewed database of allergens maintained by the World Health Organisation and International Union of Immunological Societies):

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How common is egg allergy?

A definitive diagnosis of allergy can currently only be established with a food challenge, but challenges are costly in terms of both time and resources, as well as potentially risky. So many prevalence studies measure sensitisation—using skin or blood test data—but sensitisation is not allergy. Being sensitised to something simply means that your immune system recognises it, but you may not actually react to it; in fact, many people don’t react to whatever it is they are sensitised to. Studies that use sensitisation data therefore tend to produce allergy prevalence numbers that are larger than they should be.

In a similar vein, studies that estimate allergy prevalence using questionnaires usually produce somewhat inflated numbers as people can self-report allergies that they do not actually have, although robust studies will use certain criteria to evaluate respondents’ answers and determine whether their symptoms suggest an allergy or not.

IgE-mediated allergy

The most common childhood food allergy in the world is milk, followed closely by egg. Egg allergy is thought to affect between 1 and 2 percent of children worldwide.

In 2023, a team of researchers investigating the prevalence of the 8 biggest food allergens in Europe reviewed 76 egg-related studies carried out in the whole region and calculated that around 2.7% of Europeans had been diagnosed with egg allergy during their lifetimes, generally during childhood.

In 2020, the Europrevall study—an EU-funded project covering centres in seven countries (Poland, Spain, the Netherlands, Russia, Switzerland, Greece and Iceland)—calculated that the percentage of probable egg allergy (symptoms after eating egg and positive blood test for egg-specific IgE) in school-age children ranged between 0% (Zurich) and 0.89% (Madrid).

The 2016 EuroPrevall study estimated an average prevalence of chicken egg allergy in 2-year-old European children of around 1.23%, with Greece showing the lowest (0.07%) and the UK the highest (2.18%) rates.

A Europe-wide study carried out in 2014 confirmed that egg allergy was more common in younger children than older children and revealed that it was more common in Northern Europe than in Southern Europe.

In the US, a 2020 survey of 53,575 households reported a prevalence of (suspected) egg allergy in 0.9% of all (38,408) children and 1.3% in children under 5 years old.

In Australia, eggs are the number one food allergen according to HealthNuts, a project that has been following a cohort of 5276 children from the age of 1. A 2017 study of those children put the prevalence of egg allergy among 4-year-old children at 1.2%, down from a high of 9.5% at the age of 1.

In South Africa, a study of urban and rural children around 2 years old revealed egg to be the most common food allergen, with 1.8% of urban children and 0.5% of rural children failing challenges to raw egg.

In the Middle East, the prevalence numbers are similar. A 2021 Saudi Arabian survey, 3.7% adults self-reported an allergy to egg, which was found to be the most common food allergen. A 2017 Kuwaiti study reported the prevalence of probable (convincing clinical history and a history of diagnostic food allergy testing) egg allergy as 2.1% among university students. And a 2019 review of food allergy in Iran found that egg was the 2^nd most common food allergen among food-allergic children.

In Japan, egg has also been reported as the most common cause of food allergy. A 2020 cohort study of 1713 children found that 0.8% of them were sensitised to egg white at the age of 9.

In 2019, EuroPrevall-INCO—a project including over 37 000 children which was developed to evaluate the prevalence of food allergies in China, India and Russia—reported that egg was one of the top 3 most allergic foods in Chinese school children living in Hong Kong, finding a rate of probable egg allergy (symptoms and a positive skin and/or blood test) of 0.2%. This was much higher than the rate of probable allergy in Chinese children from mainland Guangzhou (0.04%) and Shaoguan (0%), or in Russian (0.1%) and Indian (0.05%) children. Cultural differences in eating habits were put forward as a partial explanation for this finding.

Non-IgE-mediated and mixed allergies

About 2.6% of the global population is estimated to be affected by eczema, which is just over 204 million people. It’s a condition that’s more likely to affect young children and females, and food is thought to be a trigger in 20% to 30% of the cases, with the most common allergens being milk, egg, soy, wheat, peanut and fish.

Although food-triggered eczema affects children more than adults, quite a few adults still have the condition. The prevalence of food allergy in children with eczema is estimated to be somewhere in the range of 15% to 30% and the prevalence of food allergy in adults with eczema is thought by most experts to be between 1% and 3%, with between 9% and up to 24.5% of that number estimated to be new, adult-onset cases.

An international study which looked at the prevalence of food sensitisation in 2184 infants with eczema in 10 European countries, Australia and South Africa reported that egg was the most common food sensitisation in all countries and was particularly common in Australia (54%), the UK (53%) and Italy (53%) and lowest in Belgum (23%) and Poland (27%).

Separate research has also reported that egg is the most common food sensitisation in Swiss children and Swedish children with eczema, with sensitisation occurring before the age of 3.

In fact, infants who develop eczema during their first 3 months of life have been found to be more likely to develop a sensitisation to egg than children who develop eczema later in life, and the more severe the eczema, the more likely an infant is to develop a food allergy, with those with the most severe form of the condition being almost 6 times more likely to develop a food allergy than infants without eczema.

Egg is the most common food allergy among South African food-allergic children with eczema, affecting around 1 in 4, and also the most common food allergy among Korean children aged between 6 and 12, affecting about 1 in 5, and the fourth most common among children aged 12 to 15. Almost 2 in 3 Korean infants have been reported as being sensitised to egg.

In the US, egg was identified as a common food allergy among people with eczema decades ago, with a 1999 study reporting it to be the second most common food trigger in infants and children with the skin condition.

A 2016 review of the medical record of 298 American children with food allergy and eczema reported that, of the 183 children whose skin condition was likely triggered by food, 56 (30.6%) had flare-ups after eating egg, which was (still) the second most common trigger after milk.

Not everyone with eczema and egg allergy suffers from a worsening of their skin condition after eating eggs.

An early German study in which 107 children with eczema were given oral food challenges noted that the children with an allergy to egg were most likely to react and reported that just under three quarters (70%) of all the reactions were immediate, a quarter (25%) involved a delayed worsening of the eczema and the rest (5%) were a combination of both.

A 2011 study involving 11 Czech patients over the age of 14 with egg allergy and eczema reported that only 6 of them suffered from a worsening of their skin symptoms after eating egg. A similar study carried out 10 years later involving 23 egg-allergic Czech adolescents and adults with eczema reported that 3 had only immediate reactions (facial swelling, itchy skin, GI symptoms, anaphylaxis), 16 had immediate reactions and also experienced a delayed deterioration of their eczema and 4 experienced only a worsening of their skin condition.

Interestingly, the first of those Czech studies reported that 11 of the 179 (6%) eczema sufferers included in the study were allergic to egg, while the later study reported that 23 of the 100 (23%) eczema patients suffered from egg allergy, showing an increase in the number of people with both eczema and egg allergy seen at that Czech clinic over the course of the decade.

The prevalence of food protein-induced allergic proctocolitis (FPIAP) is not actually known, although it is one of the most frequent causes of rectal bleeding in children. Its reported prevalence varies widely and depends on the definition and methods of diagnosis used.

A 2021 study of 903 infants seen over a 3 year period at a clinic in suburban Massachusetts reported that 153 (17%) were diagnosed with FPIAP, based solely on the presence of blood in their stool, no possible alternative diagnosis, and a resolution of symptoms when put on an elimination diet (in this case, just milk).

However, whereas rectal bleeding is common, not all cases are due to allergy. One American study that used tissue analysis (but no food challenges) reported that about two thirds (64%) of the 56 infants they examined with rectal bleeding actually had allergic colitis. A Turkish study that used symptoms, lab tests and food elimination to diagnose their children identified 91 infants with FPIAP and reported that egg was the second most common trigger (at 37.4%) after milk (at 94.5% of the cases).

Experts do not know the exact prevalence of food protein–induced enterocolitis syndrome (FPIES) but it’s estimated to occur in the general population at a prevalence ranging from 0.015% in Australia to 0.7% in Spain and reports of cases have been on the increase in recent years, either because of an increase in new cases or because of an increased awareness of the condition among doctors.

Prevalence numbers vary per region and depend on a country’s eating culture. A 2021 review of FPIES that included studies carried out in Western countries found that between 5% (US, 2006) and 23% (multinational, 2020) of cases of FPIES in children had been reported to be caused by egg, and between 15% (Canada, 2018) and 16% (Australia, 2014) of adults cases.

In France, egg has been reported to be the second most common trigger of FPIES in children (affecting 16.2%), and in Italy, and Spain the third. In the eastern Mediterranean, egg is often the most common FPIES-provoking allergen.

In the US, a 2013 study associated around 1 in 10 cases of FPIES in children with egg, as did a 2024 study. Egg was also revealed to affect around 1 in 10 infants with FPIES in Australia in a 2013 case review, and a 2017 study found it to be the third most common trigger of FPIES in Australian infants (affecting 12%).

In Japan, egg is one of the top 2 triggers; it has been reported to be the most common trigger in a 2023 FPIES review and the second most common trigger in a single-centre study published in 2022, and cases of egg-induced FPIES have been described as experiencing a ‘dramatic increase’. Egg yolk seems to be responsible for a majority of cases.

Experts from both the US and Japan suspect that the recent rise in egg-induced FPIES may be due the change in advice given to parents asking them to introduce egg into their child’s diet at an early age (4 to 6 months) in order to reduce the infant’s risk of developing IgE-mediated egg allergy. About 8% of the American children with FPIES had reacted to baked egg, suggesting that they may have been trying the egg ladder. Although it seems to be effective for the vast majority of children, it is apparently not effective for all of them.

Cases of eosinophilic oesophagitis (EoE) have been reported to be on the increase since the turn of the century, probably because the condition is better recognised. EoE is now thought to affect 1 or 2 people in 2000 but, in people with food allergies, the number is more like 1 in 20. EoE to a food often develops in someone who already has a standard, IgE-mediated allergy to that food.

Eosinophilic oesophagitis is more common in males and can occur at any age, but it becomes more common as people get older, peaking in adults aged between 30 and 50.

The British Society for Allergy & Clinical Immunology (BSACI) states that egg may be a relevant trigger food in 35% of children and 26–36% of adults with eosinophilic oesophagitis (EoE). Egg is currently thought to be the third most common trigger of EoE in the United States, Spain, and Australia. In Iran, it has been reported as the most common trigger.

Eosinophilic oesophagitis is more common in males and can occur at any age, but it becomes more common as people get older, peaking in adults aged between 30 and 50.

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Will it go away?

IgE-mediated allergy

IgE-mediated egg allergy usually rears its ugly head somewhere between the age of 6 and 12 months—most commonly around the age of 10 months—often when a child is first exposed to egg in their diet. In very rare cases, the first reaction to egg can be quite severe.

The fact that so many infants seem to react to egg on their first taste of it implies that sensitisation to egg happens much earlier. For example, an Australian study looking into the early introduction of egg in young infants with eczema reported that the just over a third were already sensitised to egg at the age of 4 months

And a study involving 3-month old Scandinavian infants found that 7% of them were sensitised to various foods—3.7% of them to egg—before they had actually eaten any. The researchers noted an association between the foods the infants were sensitised to and the foods that their mothers were sensitised to, implying that infants of mothers with egg allergy are at greater risk of becoming sensitised to egg at an early age.

In fact, research suggests that infants can become sensitised to egg via allergens present in breast milk.

A skin prick test and/or blood test can be used to identify infants who are sensitised to egg and at risk of reacting to it the first time they eat it. Research suggests that these infants may take longer than average to outgrow their allergy.

Most children will eventually outgrow their egg allergy. However, researchers have found that the natural course of egg allergy varies a lot between populations, due in part to cultural differences in the way foods are consumed, as well as differences in study methods and subjects.

In their 2007 study on the natural history of egg allergy, American researchers reviewed the medical history of 881 highly egg-allergic patients and used an algorithm to predict the rate of egg allergy resolution. When tolerance was defined using the strictest criteria—being able to eat concentrated egg—they predicted resolution rates of 4% by the age of 4, 12% by the age of 6, 37% by the age of 10 and 68% by the age 16.

More recent studies looking at actual egg allergy resolution numbers in a range of egg-allergic children suggest a slightly more optimistic outlook, finding that at least half of the children who are allergic to egg outgrow their allergy by the age of 6.

A 2015 review of the medical records of 203 Turkish children who had been diagnosed with egg allergy and followed until the age of 6 reported that 92 (45%) had outgrown their allergy by the age of 2, 134 (66%) by the age of 4 and 145 (71%) by the age of 6. A smaller 2016 study that included 17 egg-allergic children who were followed until the age of 5 reported that 14 (82%) outgrew their allergy, on average around the age of 2.

The Australian HealthNuts study—a population-based cohort study of 5276 infants—reported in 2014 that 47% of the 140 egg-allergic children that they were following had outgrown their egg allergy by the age of 2, and in 2022 that 89% of the 323 egg-allergic children that they were then following had outgrown their allergy by the age of 6.

A 2019 study carried out in Korea reported a resolution rate of 81.5% in 124 children by the age of 3, a 2015 study carried out in Japan looked at the data of 226 children and reported resolution rates of 30% by age 3, 59% by age 5, and 73% at 6 years old, and a 2021 study of Chinese children reported that 54 of 76 (71%) children were able to eat egg by the age of 3.

A 2019 study that followed 18 South African children with eczema up to the age of 8 reported that, by the end of the study period, 13 (72.2%) had outgrown their egg allergy.

Children who develop an egg allergy at a young age are more likely to outgrow it than children who develop it later in childhood.

According to the 2016 EuroPrevall study, half of the children who had failed food challenges at the age of 2 had outgrown their allergy within a year. But as children get older, allergy resolution rates drop. However, tolerance to egg tends to keep building.

Children can generally tolerate heated egg before they can eat raw egg. A 2014 review of the medical records of 213 American children aged 3–15 months reported that half of them outgrew their allergy by the age of 6. Of the children whose allergy had not yet resolved, over a third (38.1%) were able to eat some baked egg products.

In 2022, Japanese researchers published the results of a study investigating the natural history of more persistent egg allergy. Their study initially included 137 egg-allergic children aged between 6 and 12. After taking into account the children lost to follow-up over the years, they estimated that around 1 in 7 (14.6%) were able to tolerate heated egg by the age of 7, around 2 in 5 (40.8%) by the age of 9 and just under two thirds (60.5%) by the age of 12.

Some children will end up being able to eat heated egg but will never be able to eat raw egg, i.e. outgrow their egg allergy.

Some researchers think that rates of resolution could be slowing in general and that children born in the past few years may not outgrow their childhood allergies before they reach adolescence, which means that the number of adults with egg allergy might also increase.

Certain factors can help to identify children who will not outgrow their allergy to eggs.

The inability to tolerate baked egg: several studies have shown that egg-allergic children who can eat muffins or waffles without reacting are more likely to outgrow their egg allergy than children who cannot tolerate baked egg. Similarly, an inability to eat heated egg yolk has also been associated with a smaller chance of outgrowing egg allergy.

Having systemic reactions: children who initially react to egg with skin-only symptoms—hives and/or swelling—are more likely to outgrow their allergy than children who show systemic reactions like atopic dermatitis (that is, eczema) or the involvement of multiple systems—aka anaphylaxis. Having gastrointestinal symptoms on initial exposure to egg is also not a promising sign.

Having other food allergies: children who are allergic to other foods, such as wheat and/or sesame and/or peanut and/or milk, are less likely to outgrow their egg allergy, especially if they are allergic to peanut, which often seems to go hand in hand with egg allergy. (See Good to know section later)

The results of allergy tests can also be helpful in pinpointing those who are unlikely to outgrow their egg allergy.

Large skin prick test reactions are a good indicator of a persistent allergy according to several studies, whether egg white extract, fresh egg white or egg yolk is used.

Multiple studies have also reported that blood tests showing high levels of egg-specific IgE antibodies—notably to egg white extract and/or ovalbumin and/or ovomucoid (the 2 major egg white allergens)—at baseline (when first tested) or after the first reaction to egg and each time a person is tested during childhood are ‘strongly related to persistent egg allergy’. A slow rate of decrease of these antibodies in between tests is also a sign that a child is less likely to outgrow their allergy.

The results of skin and blood tests are only applicable to people who have immediate- (IgE) type egg allergy.

Adult egg allergy

Although less common, adults also have egg allergy. A 2013 study put the prevalence of sensitisation to egg in European adults at 0.9% and a 2020 study reported that egg allergy affected between 0.02% and 0.6%. In America, the prevalence of convincing egg allergy among adults has been put at 0.8% according to 2015-2016 survey data, just 0.1% lower than the prevalence rate reported among children. Although the prevalence of egg allergy reaches its highest peak among children under 5 before decreasing, it rises again in adulthood before significantly decreasing in the over 60s.

Most adults with egg allergy are individuals who never outgrew their childhood allergy, but people can also become allergic to egg during adulthood. In fact, American data suggests that around 1 in 3 (29%) adults with egg allergy developed their condition in adulthood.

The majority of the reported cases of adult-onset egg allergy are cases of ‘bird-egg syndrome’ (see Cross reactions later) which is caused by cross-reactivity between proteins present in bird feathers and yolk and happens to people who either keep birds or work with them. Some are cases of ‘egg-egg syndrome’, which is an occupational respiratory allergy to airborne egg proteins that occurs in people who work in the bakery and confectionery industries.

However, sometimes adults just develop a classic food allergy to egg—either to cooked egg, and egg-containing foods or raw and undercooked egg —that cannot be explained.

Non-IgE-mediated and mixed allergies

There is much less data available concerning the prognosis for non IgE-mediated diseases, and what there is doesn’t inspire much hope.

First, the good news; the prognosis for infants with food protein–induced allergic proctocolitis (FPIAP) is excellent, with over half (53%) outgrowing their allergy within a year and 85% by the age of 4. Because most cases are caused by milk, milk is also the trigger food most likely to cause cases of persistent allergy.

Infants who have persistent FPIAP tend to have multiple food allergies, whereas those who achieve tolerance faster tend to be breastfed and develop symptoms at an earlier age.

When it comes to food protein-induced enterocolitis syndrome (FPIES), the news is mixed. Several studies have found that FPIES triggered by egg takes longer to resolve than FPIES triggered by milk. Timing of the introduction of the foods is thought to play a key role; milk tends to be introduced at an earlier age than egg which could explain why tolerance is also acquired at an earlier age.

A 2016 study carried out on a cohort of Spanish children found that FPIES to egg resolved in most cases, with 75% of children outgrowing their allergy by the age of 5. In France, a team of researchers using the medical records of several children with egg-induced FPIES to calculate the likelihood of resolution estimated that 3.5% of children would have outgrow their allergy by the age of 1, 40% by the age of 2, 74.3% by the age of 3, and 87.1% by the age of 5. Resolution rates were slightly lower than those to milk, but better than those to other solid foods.

In Japan, a 2022 review of 23 cases of acute FPIES in children found that around two thirds (15, or 65%) eventually outgrew their condition.

An American study published in 2022 that reviewed the cases of 203 patients diagnosed by 4 hospitals in Boston over a period of 21 years reported that egg and fish were the most common triggers in older children and that they were both associated with persistent allergy.

However, some research has found that some children with egg-induced FPIES can tolerate baked egg. A case series of oral food challenges with raw egg and cooked egg in children with FPIES also reported that tolerance to baked egg is achieved earlier (at an average age of 30.2 months) than tolerance to raw egg (at an average age of 43.9 months).

Adults can also develop delayed, non-IgE-mediated allergies to egg, like this case of food protein-induced enterocolitis syndrome (FPIES) in a 43-years-old woman who suffered from recurrent episodes of vomiting, diarrhoea and stomach pain several hours after eating eggs and egg-containing products like meringue and cake. On several occasions, the symptoms were bad enough for her to have to go to hospital.

The prognosis of eosinophilic esophagitis (EoE) seems more gloomy. A study that followed 381 children admitted to a hospital in Philadelphia with the condition for a decade or so reported that, of the 247 who were put on a long-term diet eliminating their food allergens, only 3 outgrew their allergy.

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Risk factors for egg allergy

Researchers have identified several factors which can identify the infants who are at most risk of developing egg allergy.

A family history of atopic disease—that is, some kind of allergy in at least one immediate family member—has been found to be a risk factor for all types of food allergy including egg allergy. The risk is almost doubled if more than one immediate family member has an allergy of some kind, especially if it is a sibling who has hay fever or asthma.

A family history of allergy is also associated with a poorer long-term prognosis when it comes to outgrowing egg allergy, and having a relatively high level of IgE antibodies to egg as well as a family history of allergy is also associated with a higher risk of developing an allergy to inhalant allergens.

Having eczema: multiple studies carried out in a variety of countries including the UK, Germany, the US, South Africa, Iran, China and Taiwan have linked eczema with egg allergy or sensitisation to egg.

In fact, infants with eczema are almost 6 times more likely to develop egg allergy than those without and infant boys with early eczema are the most likely to be sensitised to egg. The eczema’s onset happens, on average, about 3 and a half months before that of the egg allergy, and the more severe the eczema, the more likely the egg allergy.

This works both ways; the higher the sensitisation to egg, the more severe the eczema.

Children who are sensitised to egg are also more likely to have persistent eczema.

Children with eczema who have never eaten eggs can already be sensitised to egg and display reactions after eating eggs for the first time.

Race may also be a risk factor, according to research carried out in the US which found that Black Americans are more likely to be sensitised to a food than any other race, more likely to self-report an allergy to a food, including egg, and that Black children tend to be over-represented among children with egg allergy, in particular.

The Australian HealthNuts study found that infants with at least one parent born in Asia, as opposed to both being born in Australia, were at an increased risk of an allergy to egg, milk and/or peanuts.

And, in the UK, a 2012 study screening participants for the Learning Early About Peanut Allergy (LEAP) project found that black children were more atopic—they made more total IgE, egg white–specific IgE, and peanut-specific IgE—in their first year of life.

Race may also be a factor when it comes to acquiring tolerance; in South Africa, a study investigating the natural history of egg allergy in children with eczema revealed that children of mixed ethnicity were more likely to outgrow their egg allergy, and faster, than black Africans (90% at a median age of 82 months vs 50% at a median age of 105 months, respectively).

Finally, receiving antibiotics in the first week of life has also been found to put infants at risk of developing an allergy to egg.

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Cross reactions to chicken egg

Technically-speaking, a person can be allergic to chicken eggand another food (or foods, or aeroallergen(s)) either by cross-reactivity—the immune system mistakes the proteinin one allergen for aprotein with a similar structure inthe other—or by an independent sensitisation to each food and/or aeroallergen(a co-sensitisation or co-allergy), in which case the immune system has developed specific IgE antibodies against each allergen. It can be difficult to determine whether reactions are caused by cross-reactions or co-allergies,but the end result is the same; problems, problems.

Some people who are allergic to chicken eggs can also be allergic to the eggs of other birds. Skin test reactivity to other avian eggs is quite common in children with chicken egg allergy, with potential cross-reactivity reported in children with chicken egg allergy to the eggs of quail (70% of the children tested), duck (65%), turkey (63.5%), partridge (60%) and, less commonly, goose (46%) and pigeon (44%).

However, these sensitisations often produces no actual symptoms—they are so-called ‘clinically silent’ sensitisations. For example, a Japanese study of 20 children allergic to chicken egg found that 12 (92%) of the 13 children who were given skin tests were sensitised to quail’s egg. However, a food challenge with quail’s egg involving all 20 children found that only 9 (45%) had actual symptoms, most of which were mild. That said, a third of the children had systemic symptoms that required treatment with antihistamines, steroids or beta stimulants, and anaphylaxis to quail egg has also been reported in another study.

On a side note, some people are allergic to the eggs of other birds without being allergic to chicken eggs. For example, one case study describes a 49-year-old woman who had oral allergy syndrome, stomach pain, nausea and vomiting within 10 minutes of eating duck or goose eggs, but who had no symptoms after eating chicken eggs. And another report describes the case of a 69-year-old man who had a bad case of oral allergy syndrome after eating some duck egg white, before going on to develop breathlessness, wheezing, and skin lesions on his body. However, he could eat chicken eggs without any problem. Lab tests confirmed that both people were allergic to duck eggs but not chicken eggs.

There are also several reports of people who are allergic to quail eggs but not chicken eggs, including the case of a 54-year-old man who had been a poultry worker for 17 years and had become sensitised through contact and/or inhalationafter being repeatedly exposed to hen and quail feathers, faeces and eggs. The authors theorised that he may have developed an allergy to quail’s eggs but not chicken eggs because he only started eating quail’s eggs infrequently after he started working at the farm, whereas he had been eating chicken eggs regularly since childhood, which is a good way of maintaining tolerance to a food.

Two cases of children with life-threatening quail’s egg–provoked Food Protein Induced Enterocolitis Syndrome (FPIES) and no problem with chicken eggs have also been reported in Cyprus and Japan.

There is also something called bird-egg syndrome. This is when a person develops a secondary allergy to egg yolk after being exposed to the allergens (feathers, droppings, dander, bird blood serum) of birds, generally budgerigars, less often parrots and canaries.

Bird-egg syndrome usually manifests as primary sensitisation towards the airborne bird allergens followed by secondary/cross-sensitisation to an allergen (Gal d 5) in egg yolk. The initial symptoms (tend to include asthma, a runny nose, and red, itchy eyes before the onset of digestive symptoms—including an itchy throat, stomach cramps, vomiting, and diarrhoea.

Sometimes, sensitisation and symptoms can progress in the opposite direction: someone can be allergic to egg yolk, then maybe develop an allergy to chicken meat, and then develop asthma after becoming allergic to bird feathers. Strictly speaking, this is not a case of bird-egg syndrome, it’s just an unfortunate progression of allergies.

The first report of bird-egg syndrome came from the Netherlands, where a 65-year-old woman who got a pet parrot suddenly developed hay fever symptoms and then rashes and swelling whenever she ate eggs.

Keeping pet birds like parrots or lovebirds, or poultry like pheasants and quails and then developing symptoms to eggs and egg-containing products is the most common form of bird-egg syndrome, but people can develop an allergy to chicken meat as well.

Bird-egg syndrome is mostly seen in adults—often women—and is very rare in children, but it does happen, like the case of an 8-year-old boy who developed egg allergy because of his pet goldfinches and canaries.

Because the allergen responsible for this cross-reaction is vulnerable to heating, hard-boiled egg yolk is generally well tolerated by people with bird-egg syndrome and, indeed, by most egg-allergic people. A 2019 study that looked at data from 763 children who had failed a food challenge to egg found that 756 (99.1%) of them could eat chicken egg yolk without symptoms.

Although this type of allergy generally doesn’t go away, tolerance to raw or soft-boiled egg yolk can return over time if the person is no longer exposed to birds, as in the case of a woman who was able to start eating runny eggs and chicken cooked medium rare (yes, she does risk some form of bacterial poisoning instead) again 5 years after her budgie died.

Lab tests have shown that cross reactions between egg allergy and poultry meat are possible, but allergic reactions after the consumption of chicken tend to be rare and are often limited to oral allergy syndrome. As was the case with an egg-allergic 8-year-old boy, who developed oral allergy symptoms after eating chicken, quail and turkey meat.

People who are allergic to egg can also be allergic to the Chinese delicacy ‘edible bird’s nest’, which is made from the solidified saliva of the male Edible-nest swiftlet and generally presented in a very expensive soup. A 2001 study reported that it was the most common cause of food-induced anaphylaxis in children in Singapore and identified an allergen in egg white that cross reacted with a protein in bird’s nest.

Image by Joshua Chekov on Unsplash

Symptoms of egg allergy

Egg allergy can be IgE-mediated, non-IgE-mediated or mixed; a combination of both. These variations generally present different types of symptoms.

Immediate reactions to egg

Immediate allergic reactions are caused by IgE antibodies. These antibodies bind to certain immune system cells—mast cells and basophils—and trigger the release of histamine and other inflammatory chemicals that cause the characteristic symptoms of allergy.

Immediate reactions are the most common type of allergic reaction to egg and they range from rashes to life-threatening anaphylaxis. Reactions are different for different people, and they can also be different for the same person, varying in severity from episode to episode.

There are three main routes to developing an IgE-mediated allergy to egg, and the route taken affects the type of allergy that you get and the principal symptoms that go with it.

1. You can become allergic to egg via gastrointestinal sensitisation—i.e. by eating it. This tends to produce the ‘classic’ signs of allergy.

Although immediate-type reactions often happen within minutes of eating food, reactions to egg have been found to take longer to develop than reactions to other food. Japanese research has found that symptoms developed within 30 min for only around 1 in 3 children given food challenges to egg. This may be because egg whites contain protease inhibitors that delay the digestion of egg in children, whose digestive enzymes are not efficient enough yet to deal with them (especially when they have food allergies).

Skin reactions (namely hives and swelling) are the most common type of reaction to egg, followed by gastrointestinal reactions and respiratory symptoms.

A well-quoted retrospective review carried out in the US examined the medical data of 881 egg-allergic children diagnosed by the Johns Hopkins Pediatric Allergy Clinic and found that, during their initial reactions, 58% exhibited skin symptoms, 21% gastrointestinal symptoms, 10% lower respiratory symptoms (wheezing, coughing, difficulty breathing) and 4% upper respiratory symptoms (runny nose, stuffed nose). 18% also had eczema.

According to the British Society of Allergy and Clinical Immunology (BSACI), 80–90% of the reactions to egg involve skin (cutaneous) symptoms, including:

• hives (urticaria)
• non-eczematous rash
• swelling (angio-oedema)
• red patches (erythema)

Skin symptoms can also be produced when the skin of an egg-allergic person comes into contact with egg. Hence the advice to paediatric nurses to avoid using egg white as a treatment for nappy rash because it can cause an all-over body rash in egg-allergic infants.

10–44% of of the reactions to egg involve gastrointestinal (GI) symptoms, including:

• vomiting
• diarrhoea
• stomach pain
• bloody stool

A 2021 study looking into the differences in allergic symptoms provoked by egg yolk compared to those provoked by egg white found that children who were allergic to egg yolk were more likely to get gastrointestinal symptoms—especially diarrhoea—and less likely to get respiratory symptoms, and also less likely to require medical treatment.

Respiratory (breathing) symptoms include:

• blocked nose (nasal congestion)
• runny nose (rhinorrhoea)
• wheezing
• difficulty breathing/shortness of breath (dyspnoea)
• persistent cough
• a change in voice pitch
• hoarse voice

Asthma is often linked to egg allergy (see Good to know section later). A team of British researchers following 1218 children reported that 80% of those allergic to egg had asthma, and calculated that a child with egg allergy was five times more likely to have asthma by the age of 4 than a child who was not allergic to egg.

Asthmatics, in particular, are at higher risk for severe allergic reactions to food than other people, which is why it’s so important for someone with food allergy to try and keep their asthma under control.

A 2016 review of the medical records of 59 young children noted that egg-allergic children over the age of 2 were more likely to be diagnosed with asthma and to experience respiratory symptoms like cough and difficulty breathing than children under the age of 2.

Egg is a relatively common trigger for anaphylaxis in children. Egg has been estimated to cause anaphylaxis in about 7–12% of all food-allergic children who are admitted to hospital. Symptoms include:

• generalised rash (hives)
• pallor / low blood pressure (hypotension)
• rapid heart beat (tachycardia)
• collapse / floppiness (in infants)

An analysis of European Anaphylaxis Registry data (bringing together data from Germany, France, Switzerland, Ireland, Greece, Austria, Spain, Bulgaria, Italy and Poland) between 2007 and 2015 reported that food was the most common trigger of anaphylactic reactions in children and egg was the second most common trigger (after milk) in children under 2 years old.

The risk of egg-induced anaphylaxis differs according to local eating habits. This is nicely demonstrated in a 2019 analysis of 5 years worth of data from paediatric intensive care unit patients in North America which reported that common trigger foods for serious reactions differed according to ethnicity and region; egg was the most common trigger food affecting children of Asian descent and the second most common trigger for Hispanic children, and it was the most common trigger food affecting children living in the Northeastern US.

That said, egg is often in the top 2 most problematic triggers for very young children everywhere. A review of the medical records of children admitted to hospital in Sweden between 2006 and 2015 with food-triggered anaphylaxis, for example, reported that milk and egg were the most common triggers. On the other side of the world, two separate analyses of Korean hospital data also reported that egg was the second most common trigger (after milk) of anaphylaxis in food-allergic infants.

However, it’s not necessarily as common a trigger in older children. In the US, an analysis of anaphylaxis cases in New York between 2000 and 2014 reported that egg was the 5^th most common trigger in children under 4 years old, behind peanuts, tree nuts, seeds and milk products, but was not a common trigger in children older than that. It was responsible for 2.6% of total hospitalisations and 2.2% of emergency department visits.

Don’t panic: To be clear, the official definition of anaphylaxis is probably not what you think it is.

This means that many of the cases of anaphylaxis reported in medical studies are not actually life-threatening—when dealing with an emergency, however, since it’s impossible to predict which reactions will become life-threatening, every case of anaphylaxis should be treated as if it is potentially deadly.

According to 13-years worth of European anaphylaxis registry data, the following are typical characteristics of egg anaphylaxis in children:

• Around two thirds (61%) of children who have anaphylaxis to egg are under the age of 1, and 1 in 5 (20%) between 2 and 3 years old
• Reactions involved between 1 teaspoon or one tablespoon of egg
• About half (53%) of the children reacted within 10 minutes of eating egg, about a quarter (23%) between 10 and 30 minutes after eating egg and another quarter (24%) after 30 minutes
• Skin (notably itchiness) and respiratory symptoms (with the most obvious sign being a change in voice pitch) predominate, with GI symptoms (notably vomiting) being experienced by half the children and cardiovascular symptoms (notably a reduction in alertness) by just under half (44%)
• Children with eczema are 1.5 times more likely to have repeated episodes of anaphylaxis
• Previous reactions to egg are more likely to have been milder (in 85% of the cases)
• Around 1 in 7 reactions involved cofactors, predominantly exercise (20 cases), followed by drugs (7 cases) and stress (3 cases)

A Japanese study of egg allergy over the course of childhood found that children with prolonged egg allergy were more likely to suffer from anaphylactic events.

However, of all the childhood allergens, egg is generally the least worrisome. Most—though not all—case series report that egg rarely causes life-threatening reactions, certainly when compared to other foods that regularly caused anaphylaxis like peanuts, tree nuts or milk. In fact, according to European anaphylaxis data, egg has never led to life-threatening anaphylaxis among children, despite being the second most common trigger of anaphylaxis.

However, of all the childhood allergens, egg is generally the least worrisome. Most—though not all—case series report that egg rarely causes life-threatening reactions, certainly when compared to other foods that regularly caused anaphylaxis like peanuts, tree nuts or milk. In fact, according to European anaphylaxis data, egg has never led to life-threatening anaphylaxis among children, despite being the second most common trigger of anaphylaxis.

An international review of the mortality rate and risk factors associated with anaphylaxis concluded that, ‘Despite egg being the most common food allergy in young children in Australia, the United Kingdom, and possibly the United States, it is under-represented in documented anaphylaxis fatalities.’ In fact, there have been very few documented fatalities to egg; two children in the 1990s and one adult in the early 2000s.

Although anaphylaxis is often caused by eating egg, it can also be caused by having egg applied to the skin in an effort to dull the pain of a burn wound, for example.

In a case reported in the US, a 13-month-old boy with a known milk allergy but no other allergies was admitted to the emergency department after pulling a cup of hot tea over himself which his parents tried to treat by rubbing egg white on him which unfortunately caused an anaphylactic attack.

In a case reported in Turkey, the remedy was used on a 16-month-old infant who had spilt hot water on himself. This child had an egg allergy and asthma, but his parents didn’t realise that they should avoid putting egg on his skin as well as keeping it out of his diet. After the application of the egg, the infant’s ear and eyelid swelled up, he retched and then started to look sleepy, at which point his parents administered adrenaline and took him to hospital for treatment.

Although adults are less likely to be allergic to egg, when they suffer from anaphylactic reactions, those reactions tend to be worse. A 2019 study of food allergy among US adults noted that every 2 in 5 reactions to egg could be classified as severe and that about half of all egg-allergic adults had visited the ER because of a reaction to egg at some point in their lives, and about 1 in 5 within a year of the survey taking place.

Egg has also been reported to cause other types of severe symptoms, including acute pancreatitis, a sudden inflammation of the pancreas which generally manifests as stomach pain and can normally be treated with no lasting damage.

2. You can become allergic to egg via inhalation—i.e. by breathing allergens in. This generally results in respiratory symptoms, although it can eventually lead to the ‘classic’ symptoms of food allergy.

Although most of us tend to be exposed to egg proteins in our food, egg proteins can also sensitise people to egg via their airways. Egg is, in fact, one of the 6 most commonly reported inhaled food allergens.

Respiratory symptoms connected with egg allergy include:

• runny nose, stuffed nose (rhinitis)
• itchy, red and watery eyes (conjunctivitis, aka pinkeye)
• cough and generalised wheezing (bronchospasm)
• chest and throat tightening
• breathing difficulty

Respiratory symptoms to egg are most commonly seen in people who work with egg. This is sometimes called ‘egg-egg syndrome’.

Egg (both the white and the yolk) has been identified as a cause of baker’s asthma, which is an occupational allergy primarily suffered by people who work with grains, but occasionally a baker will develop allergic respiratory symptoms to egg protein present in the air at their workplace.

It’s not just bakers who develop a respiratory allergy to egg because of their work. Occupational asthma has also been reported in:

• workers in a food processing plant using a spray system to coat meat rolls with egg solution
• workers in an egg-processing factory (some of whom also suffered from skin reactions)
• workers at plants producing liquid and powdered egg products
• a bakery worker who sprayed cakes with liquid egg before baking
• four more bakery workers who were also exposed to egg aerosols at work
• four bakery and two confectionery workers (some of whom also suffered from hay fever symptoms) who sprayed products with liquid egg and sieved egg white powder
• and a worker in company manufacturing hen egg white-derived lysozyme for use in the pharmaceutical industry

The inhalation of egg allergens can sometimes lead to symptoms when eating egg, as was the case for some of the bakery and confectionery workers mentioned previously, as well as a lab worker who spent three years handling quail and duck eggs before having an anaphylactic attack after eating egg, and a lab technician and a research scientist who, after spending years in an embryological research facility handling chicken and quail’s eggs, started to experience itching and burning in their mouths after eating egg, as well as vomiting and wheezing. A subsequent study revealed that 4 of their co-workers had also developed an allergy to eating eggs, with all of them experiencing hives and 2 possibly anaphylaxis.

Bird-egg syndrome, described in the Cross-reactions to chicken egg section, also primarily affects people because of their work and tends to provoke respiratory symptoms to egg before a food allergy to egg yolk develops.

3. You can become allergic to egg by touching it and developing a contact allergy. This generally results in rashes but can later lead to respiratory and ‘classic’ symptoms of allergy.

3. You can become allergic to egg by touching it and developing a contact allergy. This generally results in rashes but can later lead to respiratory and ‘classic’ symptoms of allergy.

Allergic contact urticaria basically looks like hives; an itchy, a weal and flare reaction that occurs within 10 to 60 minutes of touching the food and disappears within 24 hours.

Protein contact dermatitis describes allergic (or non-allergic) eczema-like reactions to food proteins. It can be chronic or recurrent and tends to occur on the hands, wrists and arms with periods of intensified reactions when you can feel of itching or tingling a few minutes after contact with the food you’re allergic to.

Sometimes symptoms of both contact urticaria or protein contact dermatitis extend to the face, either because someone touches their face with contaminated hands or because of airborne allergens.

Contact allergies tend to be experienced by professional food handlers because they are more likely to develop when a person is continuously exposed to allergens and to things that affect the integrity of their skin, such as wet working conditions.

Like this case describing a Spanish woman with bird-egg syndrome who developed protein contact dermatitis when she handled raw poultry. She started off with itching hands and the skin then became red and scaly. The symptoms disappeared after a period of using gloves and corticosteroid cream.

Contact rashes have also been reported in formerly egg-allergic children who have gained the ability to eat eggs without symptoms but still cannot touch egg white without reacting. One explanation for this is that the digestion process becomes more efficient as we grow up and, since digestion can affect the allergenicity of egg white to a certain degree, egg might be less likely to bother older children as they eat it but can still trigger a reaction when they touch it.

Delayed reactions to egg

Delayed allergic reactions can occur hours or even days after exposure to an allergen, unlike IgE-mediated reactions that often happen within minutes. These reactions either involve diseases that rely on cell-mediated mechanisms (immune responses that do not rely on the production of IgE antibodies but instead involve the activation of T cells and macrophages which leads to inflammation and tissue damage) or by ‘mixed’ diseases that rely on both IgE- and cell-mediated mechanisms.

Delayed allergic reactions can occur hours or even days after exposure to an allergen, unlike IgE-mediated reactions that often happen within minutes. These reactions either involve diseases that rely on cell-mediated mechanisms (immune responses that do not rely on the production of IgE antibodies but instead involve the activation of T cells and macrophages which leads to inflammation and tissue damage) or by ‘mixed’ diseases that rely on both IgE- and cell-mediated mechanisms.

There are several types of delayed reactions to egg, including eczema (atopic dermatitis, AD), food protein-induced allergic proctocolitis (FPIAP), food protein-induced enteropathy (FPE), food protein induced enterocolitis syndrome (FPIES), eosinophilic oesophagitis (EoE) and eosinophilic gastroenteritis (EGE).

Eczema is a ‘mixed’ form of allergy that can produce either immediate or delayed reactions. It’s a chronically relapsing inflammatory condition that specifically affects the skin. Symptoms often occur about 24 hours after eating egg but can occur up to 48 hours later, and they look like this.

Eczema is closely linked with egg allergy (see Risk factors). Reactions to eggs in egg-allergic children with eczema often occur at first known exposure. An analysis of data from the European Anaphylaxis Registry has also found a link between eczema in egg-allergic children and a slightly higher risk of anaphylaxis.

Sensitisation to egg is often associated with a more severe and persistent form of eczema. And, although children with severe eczema will see the severity of their condition reduce over time, it will probably remain moderately severe, even if they outgrow their egg allergy.

However, as a symptom of an allergic reaction to egg, eczema only really relevant in the first year of life. If a child starts to develop eczema when they are older than 12 months, the cause is likely to be something other than egg allergy.

Food Protein-Induced Allergic Proctocolitis (FPIAP) is quite common and considered relatively benign. It mostly affects infants and symptoms generally appear within the first 6 months (often within the first month) of life. The most common symptom is blood-streaked stools (hematochezia) which is sometimes accompanied by:

• mucous in the stool
• mild diarrhoea
• stomach ache
• gas (flatulence)
• anal chaffing/pain on defecation
• refusal to eat and irritability

Otherwise, the child is perfectly healthy-looking and growth is unaffected.

Food Protein-induced Enteropathy (FPE) affects the small intestine, resulting in digestive symptoms including:

• intermittent vomiting
• chronic diarrhoea
• malabsorption (steatorrhea) which can be accompanied by a ‘failure to thrive’ (FTT), that is, a failure to show proper growth
• rarely: bloody stools

Food protein-induced enteropathy (FPE) is a subset of protein-losing enteropathy (PLE); PLE is an umbrella term that encompasses a variety of diseases that lead to excessive protein loss in the gastrointestinal tract, while FPE is a specific type of PLE triggered by reactions to food proteins.

One team of scientists has proposed the catchy term ‘food-protein induced protein-losing enteropathy’ (FPIPLE) to refer to the condition, with the following signs to identify it:

• below-average weight gain (their current weight or rate of weight gain is significantly below what is expected for their age, sex and ethnicity)
• and/or swelling (oedema) brought on by abnormally low levels of protein in the body (hypoproteinemia)
• anaemia

Food Protein Induced Enterocolitis Syndrome (FPIES) is a delayed allergic reaction to food that affects the gastrointestinal (GI) tract. There are two main types of FPIES, chronic and acute.

Chronic FPIES is quite rare and occurs mostly in infants who eat the trigger food on a daily basis. It can be recognised by intermittent vomiting and diarrhoea and, occasionally, failure to thrive (which means that a child is not getting in enough calories to reach a similar weight and size to other children of the same age and sex).

Cases of chronic FPIES in adults are vanishingly rare but not unheard of, like the first reported case of a 41-year-old woman with a 12-year history of repeated vomiting and fatigue after eating boiled eggs or scrambled eggs whose symptoms usually lasted for 3 days.

Acute FPIES is by far the most common form. In children, symptoms often occur within 2 to 4 hours after eating the offending food and can include:

• vomiting
• pallor
• lethargy
• dehydration
• diarrhoea
• shock or hypotension (i.e. low blood pressure) which can manifest as dizziness, fainting or blurred vision (as well as pallor and lethargy)

And occasionally:

• bloody stools (poop)
• fever
• intravascular volume depletion (a decrease in blood plasma volume which manifests with a rapid pulse, infrequent and low volume urination and dry mucous membranes such as a dry tongue)

A 2024 review of the medical records of 226 children with FPIES seen at an American clinic reported that all of the initial reactions experienced at home were mild.

Although more common in children, adults can also have FPIES to egg, the typical symptoms of acute FPIES tend to be different to those seen in children. They may have a faster onset and include:

• stomach pain and cramps
• diarrhoea
• vomiting
• dehydration
• transient weakness and shivering (possibly hypothermia)
• lethargy
• weight loss

The symptoms of egg-induced FPIES generally take longer to appear (around 3 hours) than FPIES to other foods (except for shellfish). People who experience severe symptoms of acute FPIES may have a longer-lasting form of the disease.

Eosinophilic gastroenteritis (EGE) is an inflammatory disorder of the gastrointestinal tract (stomach and intestine). Symptoms include:

• indigestion (dyspepsia)
• stomach pain
• nausea
• vomiting
• diarrhoea

EGE can be accompanied by other conditions, such as protein losing enteropathy (PLE) and, in one case, the condition was so severe that it was thought to have caused acute pancreatitis.

Eosinophilic oesophagitis (EoE) is an inflammation of the oesophagus caused by a food allergy, environmental allergens or acid reflux, characterised by symptoms including:

• food impaction; this is when food becoming stuck in the oesophagus which can lead to a sensation of squeezing in the chest, and can be accompanied by excessive salivation (unlike choking, a person can still breathe and talk, but they cannot eat or drink any more)
• difficulty swallowing (dysphagia)
• abdominal pain
• reflux (the flow of liquid back from the stomach into the oesophagus)
• vomiting
• heartburn (pyrosis)
• stomach pain
• food refusal

Symptoms are variable and often age-dependent. In infants, EoE tends to provoke general symptoms of oesophageal difficulties such as gagging, vomiting, feeding difficulties and weight loss, or so-called ‘failure to thrive’. Young and school-age children have symptoms that are indistinguishable from those associated with gastroesophageal reflux, such as abdominal pain, vomiting and an unpleasant taste in the back of the mouth that comes from regurgitating sour or bitter liquid. Older children and adults are more likely to have trouble swallowing and to get food lodged in their oesophagus (food impaction) and, less commonly, to suffer from heartburn.

Because symptoms can be severe, if you do suspect that you’re allergic to egg, it’s important that you see your GP/family doctor and get a referral to an allergy clinic for further testing.

Threshold for reactions

VITAL®, the Australian initiative for voluntary incidental trace allergen labelling, put out recalculated threshold doses for the ‘Big 14’ allergenic foods in 2020. Using a database containing datasets from studies carried out worldwide that used double-blind, placebo-controlled food challenges (DBPCFC), they calculated that the lowest threshold dose of protein that was needed to produce a reaction in 1% of the population allergic to egg is 0.2 mg. (Note: in this case, the ‘population allergic to egg’ is 431 people who were given a DBPCFC)

This is one of the lowest eliciting doses of the main allergenic foods. 6.3 mg was the dose needed to produce a response in 10% of the test subjects, and 94.5 mg was the dose needed to provoke a reaction in half of the test subjects.

The lowest threshold to provoke an allergic reaction to egg has been calculated at between 0.13 mg of whole raw egg and 200 mg of dried egg white.

A recent Danish study found that egg was the food most likely to elicit reactions in the most sensitive individuals at very low doses; even then, only 2 out of every 1000 egg allergic people reacted to doses under 0.5 mg of protein.

Note: we’re talking about milligrams of egg protein. The average amount of protein in a large American egg (which is equivalent to a medium-sized European egg and a large/extra large Australian egg) is around 7g.

Which means that to reach the 6.3 mg dose needed to provoke a reaction in 10% of egg-allergic people (according to VITAL®), you would need 7000mg (the amount of protein in an average-sized egg) divided by 6.3mg of an egg, which is 0.0009%, or about 1000^th of an egg. No wonder some people can have an allergic reaction to egg simply by being the same room as one (see the Good to Know section later).

Ultimately, the threshold dose needed to provoke symptoms varies widely between people. It also varies per person, depending on the circumstances around the meal.

Your threshold can be lowered and your allergic reactions worsened by things called ‘cofactors’. Cofactors include things like how much a person eats and whether those ingredients have been cooked or processed.

For example, raw or undercooked egg can trigger more severe reactions than well-cooked egg. And baking an egg with wheat can reduce its allergenicity further, if it’s baked for long enough at a high enough heat. Which are properties that the egg ladder is built on.

Other types of cofactors include exercise, anti-inflammatory drugs, alcohol, infection and stress. Egg has been specifically implicated in cases of food-dependent exercise-induced anaphylaxis (FDEIA).

Cofactors are thought to play a role in about 14% to 30% of all anaphylactic reactions.

Please note: the amount of egg needed to provoke a reaction says nothing about how severe the reaction will be. And, even if your reactions have been mild in the past, that does not mean that they will continue to be mild.

Image by Ivan Samkov on Pexels

Diagnosing egg allergy

A diagnosis of egg allergy will primarily be based on your clinical history—a record of consistent symptoms following the consumption of egg or egg-containing foods. This will require you to provide your allergist with answers to questions about your general medical background (including any other allergies you may have and relevant illnesses in your family) and your dietary history (what you ate to provoke your symptoms, what those symptoms were, how long they lasted, whether you had exercised or taken painkillers and many other details).

It would be handy to specify which form(s) of egg you (or your child) can’t eat, if applicable; cooked (e.g. hard-boiled egg, cake, waffle), partially cooked (e.g. scrambled egg, poached egg, quiche) or raw (e.g. mayonnaise, steak tartare, protein shake).

Your medical history determines what comes next; on the basis of your answers, the allergist will try to determine what type of allergy you have—a primary, immediate-type allergy, a cross-reactive allergy or a delayed-type allergy—or whether it could be something else, and this will determine the tests they ask for to come up with a diagnosis.

Diagnosing IgE-mediated reactions to egg

Skin tests

An IgE-mediated sensitisation to egg is typically confirmed by a skin prick test, which involves someone placing a small sample of egg extract or raw egg (often using egg white) onto the skin (generally the forearm of an adult/older child or the upper back of a young child) and pushing it through the top layer of skin by pricking it with a lancet. It takes about 15 minutes to see a reaction (or not). On incredibly rare occasions, skin prick tests can cause serious reactions.

This test is often carried out first because it is quick and simple to perform and gives rapid results, but it is generally used to rule out an allergy rather than to confirm one, because it has excellent negative predictive value—if the skin weal is under a certain size, you are highly unlikely to have an allergy—but poor positive predictive value—the skin weal has to be very large before an allergist can say with any kind of confidence that you probably have an allergy.

The accuracy of the skin prick test is limited by the fact that the processing of commercially-made allergen extracts tends to destroy the heat-sensitive allergens. In such cases, someone could get a false negative result and be wrongly told that they are not allergic to egg.

One solution to this problem is the prick to prick test. This test is very similar to the skin prick test, except first the lancet is used to puncture fresh food and then it is used to prick your skin. When the food is in liquid form, the technique is actually the same as the one used for the skin prick test and, when the food is solid, it’s often ground down and put in saline solution.

The prick to prick test often produces superior results to commercial extracts because the fresh food used should contain all of the allergens that a person can react to. The lab used by the clinic can also prepare the extract in specific ways which may add to its efficacy.

Over the years, scientists have tried to define weal diameters—using both fresh egg and commercial extracts—beyond which a person is likely to fail a food challenge to egg. These values, together with a convincing clinical history, are generally used to establish a provisional diagnosis of allergy without the need for an oral food challenge. Cut-offs have also been established for egg-sensitised infants who have never eaten egg before below which they are likely to pass an egg challenge and be able to incorporate egg into their diets.

However, although some research has found that skin prick testing is more reliable than blood testing in diagnosing egg allergy (at least children under 2 years old), it is not infallible; for a start, it is possible to have no response (i.e. no skin weal) and still have a positive reaction to egg, and skin tests have also been found to be poor predictors (4) of tolerance to baked egg, so an oral food challenge will always be needed to confirm a person’s allergic status.

Blood tests

Sometimes, the doctor may decide to order a blood test, aka an immunoassay. Perhaps the skin prick test was inconclusive, or the suspected allergen is not available for skin prick testing, or you’re unable to undergo the test for some reason.

A blood test involves having a small sample of blood drawn so that it can be sent to a lab where technicians will use allergen extracts to check whether there are IgE antibodies in your blood that react to them. It can take 1 or 2 weeks to get the results.

Blood tests can be less sensitive or specific than skin tests, but they have other advantages: they are perfect for people who cannot stop taking certain medications or have extensive skin disease or tattoos, and they can safely be used on infants, squirming toddlers and people who are at risk of suffering an anaphylactic reaction.

Blood test panels also typically include a whole range of potential allergen extracts including other foods or aeroallergens that the allergist may want to check your reaction to.

For more specific information, a component blood test—aka Component Resolved Diagnosis (CRD)—can be carried out. Instead of using extracts of whole foods containing only (heat-stable, plentiful) allergens, the CRD tests the reaction of IgE antibodies in your blood to isolated, individual proteins. This improves the diagnostic sensitivity of the test as allergens that would otherwise be missing from the whole food extract or exist only in tiny amounts are present in concentrated form in the CRD test.

This type of test enables the doctor to see exactly which allergen(s) you react to, which allows them to determine whether you are sensitised to cross-reactive allergens that are unlikely to produce symptoms, and whether you are sensitised to certain allergens that could affect your management plan.

For example, if you’re sensitised to a heat- and digestion-stable egg protein like Gal d 1 (ovomucoid), you’re at risk of having more serious allergic reactions, and your allergy is more likely to be persistent. But if you’re sensitised only to protein that is vulnerable to heat and digestion like Gal d 2 (ovalbumin, found in egg white) or Gal d 5 (chicken serum albumin, found in egg yolk), you will be able to eat either egg yolk or egg white, you can probably eat heated—cooked, boiled, or fried—eggs, and you will probably have milder reactions.

Component blood tests are also made up of very large panels of allergens which include many other foods and aerollergens that the allergist may want to check your reaction to and can help to determine whether or not a sensitisation to a cross-reactive allergen will be symptomatic or not.

Unfortunately, although CRD could potentially reduce the need for oral food challenges and contribute to tailored management plans, it’s not yet considered a routine diagnostic method and it’s not comprehensive; the most widely used tests neither contain all of the identified allergens (which are also not all of the possible allergens), nor are they universally available. Testing for certain specific egg allergens would require special preparation and is therefore only likely to be done for research purposes.

Additionally, as it is with skin and standard blood tests, CRD is better at confirming an allergy than at eliminating the possibility of one. And, because sensitisation patterns differ according to geography and populations, with different allergens being more important in different regions and in people of different ages, allergists need to understand their patient populations so that they interpret the results of the tests correctly.

As with skin testing, scientists have tried to find ways to use blood tests to predict the likelihood of experiencing symptoms after eating egg, as well as how severe those symptoms may be in an effort to avoid having to undertake a food challenge.

Researchers have determined levels IgE antibodies to egg white and ovomucoid (Gal d 1) that can predict the likelihood of a reaction to raw or cooked egg white, what levels of specific IgE antibodies to Gal d 1 and/or Gal d 2 levels could predict the risk of anaphylaxis to egg.

However, as with skin tests, blood tests are not infallible; values can differ between tests made by different manufacturers, the predictive ability of the cut-off values varies by age group some people who show levels that are suggestive of no allergy can still have allergic reactions (even anaphylaxis), and blood tests are not reliable when it comes to predicting tolerance to baked goods, so a food challenge will always be needed to establish a definite diagnosis.

Nevertheless, blood tests are still used to monitor the progression of egg allergy, with falling levels of sIgE to egg white and ovomucoid indicating that a child is outgrowing their allergy and certain levels of specific IgE antibodies to egg white and/or ovomucoid suggesting that the allergy is persistent.

When a child does not look like they will outgrow their allergy, blood testing can also help to identify patients who would be suitable candidates for immunotherapy, which is no small consideration since immunotherapy treatment, while potentially life-changing, is a costly process in terms of both time and resources.

A positive skin or blood test does not mean that you are allergic to something. While skin prick tests and blood tests help with diagnosis, positive results only show sensitisation to specific allergens. Being sensitised to a food doesn’t mean that you’re allergic to it and that you will develop any symptoms.

In this study, for example, a team of American doctors decided to determine how often elimination diets based solely on lab tests were actually justified. They looked at the medical data of children who had tested positive for a sensitivity to a food and had been been told to avoid those foods. When those children were subsequently given oral food challenges, the vast majority of them turned out not to be allergic after all, and 84% to 93% of the foods being avoided were able to be reintroduced into their diets. In the case of the 10 children who had tested positive for a sensitivity to egg, only 1 of them actually had reactions after eating egg.

A positive test result simply means that your immune system is specifically aware of an allergen or allergens in that food. Why some people later develop an allergy to that food, and some do not, is not yet known.

Neither can the results of your blood or skin test tell you how much egg you can eat before you have a reaction—i.e. what your threshold is—or predict how severe that reaction may be; having a large skin weal in response to a prick or a high level of IgE in your blood does not necessarily mean that you will have a serious allergic reaction if you accidentally eat some egg hidden in a meatball.

Food challenge

The only way to get a definitive diagnosis of egg allergy, and to have some idea of what your reactions might be like and how much is needed to provoke them, is to undergo an oral food challenge. This generally involves eating a very small amount of egg, waiting for a reaction, and then doing it again, gradually increasing the dose until an objective—visible—reaction occurs or a maximum dosage is reached. It can take around 4 hours, depending on the type of challenge undertaken and the length of observation time needed.

You can read more about oral food challenges here.

Oral food challenges for egg can include the whole egg, just the yolk or just the white, and the egg can either be given in a raw or cooked form.

Oral food challenges are generally undertaken either when someone’s history and their test results disagree (i.e. they have negative tests results but their history strongly suggests an allergy, or vice versa) or to check whether someone has outgrown their allergy to ensure that they don’t unnecessarily restrict their diet or worry about hidden allergens in processed foods.

Practically speaking, most people do not undergo this kind of test since it requires a lot of time and resources. And oral challenges are rarely, if ever, offered to people whose history includes severe reactions to a suspected food. Whenever possible, allergy diagnoses are based on a combination of medical history and lab tests.

Because of the risk of severe reactions, oral food challenges should only be done by an experienced consultant in a medical setting.

In 2015, a study that specifically looked at the outcomes of oral food challenges to egg compared to those of the other main problematic foods (i.e. milk, wheat, soy, egg, peanut, seeds, tree nuts, fish and shellfish) compiled data from all the challenges carried out at The Children’s Hospital of Philadelphia between August 2004 and December 2014 and found that failed egg challenges tended to produce more gastrointestinal symptoms and less respiratory symptoms than challenges with other major food allergens (like milk and peanut), but that around 1 in 4 children had quite serious reactions.

Severe reactions—e.g. to baked egg—can be delayed by up to an hour after eating the egg, which is why oral food challenges for some people may include a prolonged observation period after the test period.

That said, food challenges for egg are no more likely to produce bad reactions than challenges for any of the other major allergens—in general, although around a quarter of the children who undergo a challenge to egg will have a bad reaction, they are generally treatable during the exam and none require hospitalisation.

Most children will probably receive a clinical diagnosis without having to undergo a food challenge if they have a clinical history of reacting after eating egg-containing food coupled with a high level of egg-specific IgE antibodies.

Although food challenges help to diagnose food allergies and identify a suspect food, there are other reasons to undergo food challenges, namely:

• to identify culprit foods in cases of allergies to multiple unknown foods
• to determine a patient’s threshold—how much egg they can eat without reacting—so that dietary advice based on the outcome of the challenge can be given
• to confirm the development of tolerance to egg
• to allow some egg-allergic patients to include some form of egg—e.g. baked egg, or heated egg yolk—in their diets

As the majority of children who are allergic to egg are expected to grow out of their allergy, they may be asked to undergo follow-up food challenges in order to determine whether the allergy has resolved and they can reintroduce egg into their diet. In general, you can expect your egg-allergic child to be rechallenged every 6–12 months but the timing of the challenges will depend on their history of reactions and lab test results and will only happen if they have not had any recent reactions.

Children who have reacted to very small amounts of egg, have had severe reactions in the past and have a high levels of egg-specific IgE antibodies in their blood and who are older than the average child with egg allergy will not be expected to outgrow their allergy quickly and are more likely to rechallenged later rather than sooner.

Challenge protocols can also be adapted to suit the needs of patients. Japanese doctors have recently come up with a three step oral food challenge for children to test the major food allergens. It involves challenging each child first with a low dose of the food then, if they pass this first test, trying a medium dose within the next 12 month period and, if they pass this test, trying a maximum dose within the next 12 month period. Children who are suspected of having a severe allergy start first with a very low dose before trying the low dose amount. Each time a child passes a challenge, they are able to incorporate the amount of egg they tolerated into their diet until their next challenge.

In this way, children who are not be able to tolerate the maximum dose off egg immediately can still include some egg in their diet as soon as possible and build up their tolerance to it, which has been shown to enable them to eat a full dose of egg during a food challenge at a later date, especially if they are under the age of 4.

If your allergist offers to give your child an oral food challenge to egg, you should definitely consider taking them up on their offer; research has shown that parents who watch their child undergo a challenge to egg benefit from the experience, no matter what the outcome. Those whose child passed the challenge are obviously happy to know that their child will not have to worry about any further reactions and are able to confidently relax their previous rules around eating.

But those whose child fails a challenge are still better off than those whose child never took the challenge in the first place; the certainty they get from having a definite diagnosis and seeing how their child reacts perhaps counter-intuitively makes them less stressed about things like making arrangements for their child to eat outside the home and about how severe the allergy is and how much they need to change their lifestyle to accommodate it, as well as about how other people will treat their child.

Oral food challenges have also been used to facilitate the re-introduction of egg into the diets of children with previous egg allergy. In this case, the parents of children who have passed a challenge to heated egg are instructed to keep feeding their child that amount at least four times per week for 5 to 8 weeks before being introduced to a larger amount under medical supervision and, if that challenge is passed, eating that larger dose for 5 to 8 weeks before the next challenge. If a challenge is failed, the child continues to egg the amount of egg they could tolerate for a few more weeks.

Doctors have found that increasing the dose under medical supervision is a safe and effective method of facilitating egg reintroduction that can be faster than using an egg ladder because it gives parents the confidence and structure they need to keep increasing the amount of egg that their child is eating until they gain full tolerance or are at least able to incorporate a certain amount of egg into their diets on a regular basis.

Diagnosing non IgE-mediated and mixed reactions to egg

Non IgE-mediated diseases are difficult to diagnose for several reasons, not least of which is the fact that IgE testing is often of no use. This makes the clinical history especially important for the diagnosis of these types of conditions. Even then, the symptoms are not easy to connect to the actual meals because of the time delay, and the symptoms associated with digestive allergies lack the skin and respiratory signs that doctors usually associate with allergy.

Skin tests

Eczemais diagnosed based on personal and family history of allergy and a skin examination. While there are no standard diagnostic criteria, there are certain features that a doctor can look for to diagnose it.

That said, these criteria are based on the characteristics of paediatric eczema, which is not the same as the manifestation of eczema in adolescents or adults, making diagnosis of eczema in older age groups more challenging. Sometimes people with eczema in these age groups will have to undergo additional tests to rule out other diseases first, and a skin biopsy may be needed before a diagnosis of eczema is made. However, these differences are now being taken into account and guidelines are being updated.

Once the diagnosis of eczema is made, efforts will first be made to try and get the skin condition under control using topical skin creams and drugs before any further testing is done. Generally, only if the skin is not getting any better will tests be carried out to see whether allergens, like food, could be aggravating the condition.

The identification of potential food allergens is generally done by looking for specific IgE antibodies to a food using skin prick tests or blood tests (the latter is often used if the skin condition is too bad for a skin test, or medications are being taken that will interfere with the results, or if the tests involve a young infant).

In cases of delayed symptoms, doctors may use the atopy patch test (APT). This test generally involves walking around with food (either fresh or in solution) contained in tiny aluminium capsules taped to your back for up to 3 days and having your skin checked for a reaction after 48 hours and 72 hours.

Atopy patch tests have been carried out with varying degrees of success to diagnose food allergy in people with eczema—showing, alternatively, a sensitivity higher than that of the skin prick test, a high false negative rate and excellent predictive value.

However, when used In combination with a skin prick test, a negative result for both tests is a reliable indicator that a child is not allergic to egg and will probably not need to be challenged.

The atopy patch test has also been used to try and diagnose delayed digestive allergies, with mixed results; in the case of food protein–induced enterocolitis syndrome (FPIES), for example, it has proven itself to be both ‘a promising diagnostic tool for the diagnosis of FPIES’ and ‘not helpful in identifying the [trigger] foods’, while showing ‘poor utility in the follow-up prediction of outgrowing FPIES in children’. With food protein-induced allergic proctocolitis (FPIAP) and food protein-induced enteropathy (FPE), it has shown low sensitivity and with eosinophilic oesophagitis (EoE), it has shown that it can ‘identify potential causative foods’. For these diseases, it is not the diagnostic instrument of choice.

A skin application food test (SAFT) may be used instead for children under the age of 4. It’s basically the same thing, but the capsule of food is only applied to the skin for 10 to 30 minutes. It also has mixed results, having been described as reliable and child-friendly, good enough to render the APT test superfluous and not adding anything useful to the diagnostic process when a skin prick test has already been done (although this latter study was carried out on a very small group of children, none of whom may have had a non-IgE-mediated form of egg allergy).

Elimination diets and food challenges

While skin tests may provide an indication of sensitisation, they cannot diagnose a food allergy; that has to be done with a food challenge during which the doctor can see whether or not, in addition to the immediate reactions, the suspected food also produces a worsening of the skin symptoms within the next 48 hours (often within a day). If it does, the food can then be eliminated from a person’s diet and their skin condition will be monitored for the next few months to see if there is a persistent improvement. When more than one food is suspected, the next challenge will be done a few weeks after the first one.

The diagnosis of delayed digestive allergies generally starts with exclusion; first other possible causes of the symptoms are eliminated and only then will the suspected food(s) be excluded from a patient’s diet—and, if they are breastfeeding, from their mother’s diet, too.

If the symptoms disappear, the first step towards a diagnosis involves reintroducing the foods one by one into the diet and seeing if the symptoms return. If the symptoms don’t disappear, it could be that the diet has not been restricted enough or that other foods should (also) be considered for elimination. Or it could be that something other than an allergy is responsible, in which case, the allergist’s job ends and another specialist’s begins.

When it comes to food protein-induced allergic proctocolitis (FPIAP), as it’s generally quite a benign condition, the allergists may want to wait for 2 to 4 weeks to see if the condition goes away by itself. If symptoms persist, a diet that eliminates the offending food should cause them to go away, often within 72–96 hours. The food can be (briefly) reintroduced into the infant’s diet 1 to 2 months later to (unofficially) confirm the diagnosis once symptoms reappear. Theoretically, an oral food challenge is necessary to officially confirm the diagnosis but, in practice, this isn’t done if the infant looks otherwise healthy.

The diagnosis of food protein-induced enteropathy (FPE) relies on seeing how a patient responds to an elimination diet and then performing an endoscopy and biopsy to check on the state of the small intestine. If the right food is eliminated, the symptoms should disappear and the tissue samples should look normal within 1 to 4 weeks.

The diagnosis can be confirmed by an oral food challenge, which essentially involves reintroducing the food into the diet 1 or 2 months after it was eliminated (which can be done at home if previous reactions have not been severe). If the food produces vomiting and diarrhoea within 1.5 to 3 days after being eaten, the diagnosis is confirmed and it can be taken out of the diet. Most children outgrow the condition by the time they’re 2, sometimes 3 years old.

The diagnosis of food protein induced enterocolitis syndrome( FPIES) mainly relies on a person’s clinical history and symptoms appearing when the offending food is reintroduced after an elimination diet.

In the case of chronic FPIES, an elimination diet should result in the symptoms going away within 3 to 19 days. Reintroducing the trigger food should produce the symptoms of acute FPIES—i.e. projectile vomiting—which should be enough confirmation.

n the case of acute FPIES, eating the offending food should be followed by symptoms that should fit specific diagnostic criteria including copious vomiting within 4 hours. Although confirmation of the diagnosis officially requires an oral food challenge, because it often produces nasty symptoms that the patient quite rightly has no wish to suffer through, in practice, this is rarely done and challenges for the diagnosis of chronic FPIES are more common.

However, since FPIES symptoms tend to be different for adults with acute FPIES and there are no strict diagnosis guidelines for them, oral food challenges are often necessary.

There are other reasons to undergo food challenges in cases of FPIES, including:

• identifying a culprit food in cases of allergies to multiple foods
• confirming the development of tolerance to a trigger food, which is often done between 12 to 18 months after the most recent reaction

Many clinics will only carry out a food challenge in an infant to see whether they have outgrown their allergy.

Although oral challenges normally provide a measure of certainty as far as food allergies are concerned, a team of Spanish and Italian doctors have warned that around 1 in 8 of their paediatric patients have passed an oral food challenge to egg only to react to it when exposed to it again at home the following day. They have therefore suggested that anyone with suspected FPIES to egg and a history of severe reactions be given more than one supervised challenge, just to make sure.

Although the majority of people with FPIES will have negative skin or blood tests to their trigger food, in some cases people do have an IgE sensitisation too. This is called ‘atypical FPIES’ and it affects between 1 in 4 and 1 in 8 people with FPIES. According to American research, the foods most commonly associated with this type of FPIES are egg, milk and peanut, but this may just be because those are the foods most typically eaten by American children (who make up the bulk of these studies). A person can have atypical FPIES to several foods, and those foods can include anything, from shrimp to avocado.

Some children with atypical FPIES may take longer to outgrow their condition (if, indeed, this happens at all) or may develop a classic IgE-mediated food allergy with potentially more dangerous symptoms. As such, periodic testing for an IgE sensitisation is advised in children who also have an IgE-mediated food allergy to other foods or suspected food-induced eczema.

When diagnosing eosinophilic oesophagitis (EoE), first other conditions that produce similar symptoms, like gastroesophageal reflux disease (GERD), are eliminated as a possibility before any intrusive testing is done. Then, if eosinophilic oesophagitis is still suspected, an upper GI endoscopy (aka an oesophagogastroduodenoscopy) and biopsies are carried out to look for specific levels of eosinophils in the oesophageal tissue (15 or more eosinophils per high-powered field, to be precise).

Standard elimination diets for cases of EoE are often based on the most common causes of the disease, either ‘2 food diets’ (dairy and wheat), ‘4 food diets’ (dairy, wheat, egg, and legumes) or ‘6 food diets’ (dairy, wheat, egg, legumes peanuts/tree nuts and fish/shellfish). These are called ‘empiric’ diets, i.e. diets that are based on observation and experience. The diet can be made less cumbersome by starting small, first with one food (i.e. milk) or two foods and then eliminating more foods if the symptoms don’t disappear.

The empiric diet approach is not the only approach. Sometimes the foods to be eliminated are determined using lab tests—atopy patch test and SPT and/or blood test—first (a targetted approach). Both methods work equally well for both children and adults although the targetted approach has the advantage of often requiring the elimination of fewer foods. That said, a lot of people with EoE don’t have any measurable IgE antibodies to their trigger food, so the targetted approach can only help some.

The diet normally takes about 6 weeks. If the symptoms go away and the tissue samples look good, the trigger is assumed to be one or more of the foods that was eliminated. In order to pinpoint the trigger(s), each food is reintroduced back into the diet one by one. If a reintroduced food causes symptoms to return and/or biopsy specimens to look abnormal, then it is identified as a trigger food and must be eliminated from the diet indefinitely. (In the real world, children may balk at undergoing so many intrusive tests or there may not be the capacity to perform them, in which case, they will probably not be required for a diagnosis.)

The diagnosis of eosinophilic gastroenteritis (EGE) involves a similar approach, but focussing on the stomach instead of the oesophagus.

Elimination diets are best performed under expert guidance, because there is a risk that excluding a food from your diet because you think that you may be allergic to it or because it causes mild or delayed symptoms (1) can lead to you developing an IgE-mediated allergy to that food, often with severe—sometimes fatal—reactions.

The good news is that, when a delayed digestive allergy is diagnosed, excluding offending food(s) from the diet leads to the resolution of symptoms and the repair of the underlying tissue damage in most children and adults, and improves quality of life, even though the diet may be difficult to stick to. When it comes to young children, if staple foods are being eliminated, dietary guidance may be needed to ensure normal growth and development.

Image by John Carlo Tubelleza on Unsplash

Image by Jakub Żerdzicki on Unsplash

Good to know

Although egg allergens have been found in breast milk, mothers of infants with egg allergy are not advised to follow an egg-free diet.

Both major egg allergens (ovomucoid and ovalbumin) have been detected in breast milk, and a dose-response relationship has been demonstrated, with each extra egg eaten per week resulting in an average increase of 25% in the concentration of ovalbumin. Egg proteins have been detected in the breast milk of lactating women up to 8 hours after eating egg, with the amount of allergen in the breast milk peaking around 4 to 6 hours after eating.

However, the amounts of egg protein detected are measured in nanograms (a billionth of a gram, or 10⁻⁹, which is 0.000000001 g) or picograms (a trillionth of a gram, or 10⁻¹², that’s 0.000000000001 g), which is unlikely to cause an IgE-mediated reaction, and not all women seem to produce breast milk with egg protein after eating eggs; one study detected no egg protein in the breast milk of 1 in 4 women, and another found none in the breast milk of a third of their subjects.

Some research has found that a strict egg-free diet doesn’t seem to make much difference to the amount of allergen that an infant is exposed to during pregnancy or soon after, anyway.

Current European and UK guidance is underpinned by World Health Orgnisation (WHO) advice and recommends that mothers who are able to breastfeed their child until around the age of 6 months do so without avoiding any foods, and certainly nutritious staple foods like egg, because it’s important that they have an adequate diet themselves, and infants are rarely sensitive enough to react to the extremely low levels of allergens in breast milk. On balance it is felt that avoiding those foods may do more harm than good.

An egg-free diet during lactation should only be considered if:

• An infant has persistent eczema which does not respond to topical treatment, and egg is a known of suspected trigger
• An infant is suspected of reacting to the egg in their mother’s diet

In which case, an egg-free diet should only be attempted for 4 to 6 weeks, before egg is reintroduced to make sure that the diet is working.

Maternal dietary avoidance of egg is not recommended for the prevention of food allergy, either. A 2023 trial carried out in Japan that included 380 breast-fed newborns showed that a maternal egg-free diet made no difference to the development of egg sensitisation or egg allergy during the first year of life.

In fact, Australian research suggests that the presence of egg proteins in breast milk promotes oral tolerance and is associated with a decreased risk of developing IgE-mediated egg allergy, finding that infants exposed to breast milk containing detectable ovalbumin were half as likely to be allergic to egg at the age of 1 than children who were not exposed to egg-containing breast milk, and a third as likely to have developed egg allergy by the age of 2 and a half.

Having an egg allergy is associated with a higher risk of developing a sensitisation to aeroallergens and/or developing respiratory diseases.

A Japanese study followed 108 infants until the age of 5 and found that a high level of egg-specific IgE antibodies when they were 6 months old was a significant predictor of an allergy to dust mites at the age of 5.

A German study followed 1314 infants in five German cities from birth until the age of 3 and found that infants who had egg-specific IgE antibodies at the age of 1 were at a higher risk than the others of developing a sensitisation to indoor (mite and cat) and/or outdoor (tree and grass pollen) allergens by the time they were 3 years old. A history of allergy running in the family increased the risk all the more.

A British study following a cohort of 1218 children from birth reported that being allergic to egg in infancy increased the risk of aero-allergen sensitisation in early childhood, especially when the child eczema, too.

And a Czech study of 288 men and women with eczema found that those who had IgE antibodies to egg white and/or egg yolk were more likely to be sensitised to dust.

The combined sensitisation to both food—especially egg—and inhalant allergens increases IgE antibody production and the risk of developing allergic respiratory diseases.

Research has noted a strong link between egg allergy and hay fever with some studies reporting up to 4 in 5 egg-allergic children suffering from this respiratory condition. Children with egg allergy and hay fever have also been found to take longer to outgrow their egg allergy.

Multiple studies have also found a link between egg-allergic infants and asthma. In fact, although asthma is linked to several types of food allergy, children with egg allergy are more likely to have asthma than children with other food allergies.

Whether the egg allergy is transient or persistent, children who test positive for sensitisation to egg at one year old are twice as likely to have asthma by the time that they are 4 years old than children who are not allergic to food. Testing positive for a sensitisation to egg at one year old is also linked to having asthma at age 7, and during adulthood.

Children with egg allergy and asthma are also more likely to take longer to outgrow their egg allergy, if indeed they outgrow it at all.

And, even when children have outgrown their egg allergy, they are still at risk of developing asthma, according to a study of South African children with eczema and egg allergy that reported that, at the time of diagnosis, 3 of 13 (23%) of the children who later outgrew their egg allergy had asthma and 4 of 5 (80%) of the children whose allergy persisted allergy had asthma. However, when the researchers followed up on the children at a later date, though there was no change in the asthma status of the children with persistent egg allergy, 4 more of the children who had outgrown their allergy now had asthma, too.

Airborne egg proteins may be more of a problem than you might think.

Although most of the reports of egg allergy via inhalation come from the workplace, inhaling egg allergens at home has also been reported to cause problems, including the case of a 6-year-old boy with multiple food allergies who would get hives when simply being in the vicinity of an uncooked egg (described here) and the case of a 9-month-old infant who started wheezing and vomiting and developed a rash while in his mother’s arms after she had eaten egg, and then suffering an anaphylactic attack while in the arms of his older sibling after she had eaten an egg.

Egg allergens can also be found lurking in people’s homes in potentially problematic amounts. This was first shown in a 1995 Dutch study which sampled the dust from 11 houses and found egg proteins in each one at levels high enough to cause sensitisation and/or symptoms.

In 2014, a Norwegian study found egg allergens in the mattress dust of 22% of the 143 homes they looked at. They were more likely to be found in those of girls than of boys, possibly because of the former’s tendency to put teddies and decorative pillows on their beds—aka ‘dust and allergen reservoirs’. Other risk factors for having more egg allergen in mattresses included the size of the home (the smaller the dwelling, the more egg dust was likely to be found in the mattress) and having bedrooms and kitchens on the same floor.

4 years later, a German study found egg proteins in dust samples taken around the eating areas and bedrooms of all the households they examined. It may be possible, as it is with peanut, that these allergens could sensitise a child to egg through their skin.

Having an egg allergy is associated with a high risk of developing another food allergy.

Most people with food allergies are allergic to more than one food, and it’s no different for people allergic to egg. However, egg-allergic children are even more likely to be allergic to multiple foods. They are, for example, twice as likely to develop an allergy to sesame or soy than children with other food allergies.

Having an egg allergy is associated with an especially high risk of developing peanut allergy. One of the allergies most often associated with egg allergy—and also the most common childhood food allergy—is milk. But while it’s not that surprising to find that children who are vulnerable to food allergies often have the two most common ones, what’s more of a surprise is that egg-allergic children are often more likely to develop peanut allergy.

In fact, several studies have shown that egg-allergic children actually have a high risk of becoming allergic to peanuts.

This is especially obvious during early childhood. As part of the British and American LEAP (Learning Early About Peanut Allergy) project, one study focused on trying to identify British infants who had the highest risk of being allergic to peanuts. It reported that the two most important risk factors for becoming sensitised to peanuts were egg allergy and severe eczema. Because eggs and peanuts do not share similar proteins, cross-sensitisation was considered an unlikely explanation for the connection. But both egg and peanut allergy share severe eczema as a risk factor for becoming allergic, suggesting that they are connected through the method of sensitisation—food allergens getting through a broken skin barrier.

A large American study which examined the medical records of 881 of egg-allergic infants who were followed for almost 5 years reported that just over 9 in 10 (93%) had another food allergy, the most common being peanut, which was present in 3 of 4 (75%) of the infants. The children with multiple food allergies took longer to outgrow their egg allergy than the children who were only allergic to one food.

As children get older and outgrow some of their food allergies, the link between egg and peanut allergy remains strong, American national survey data gathered between 2015 and 2016 reported that, of the roughly 346 children (0.9% of 38,408) with egg allergy, just under 2 in 3 (60.2%) were allergic to multiple foods and around 1 in 3 were allergic to peanut.

A sensitisation to peanuts is may be more likely if an infant’s mother eats peanuts while she is pregnant. And if the mother eats eggs every day during her pregnancy, her infant is more likely to be sensitised to egg and allergic to peanut.

However, a possible solution to the problem of both egg and peanut allergy may be the introduction of both these foods into an infant’s diet. (see later)

An egg allergy can take different forms across time.

For example, sometimes children with chronic FPIES end up developing acute FPIES and this form of FPIES can, in turn, develop into an IgE-mediated form of allergy. Sometimes this goes the other way around and children can develop FPIES to egg after outgrowing their IgE-mediated allergy and reintroducing egg into their diet.

You can develop an allergy to egg after an organ transplant.

Although it can happen after different types of transplant, the liver is by far the organ most likely to provoke a new food allergy, and an allergy to egg is the food allergy you’ll most likely get.

Children are much more likely to develop an allergy after a liver transplant than adults; in fact, there are case reports describing children and adults getting a liver from the same donor and the child developing a food allergy while the adult does not. Why this is so is not known, although it may be something to do with the fact that the child needs a liver transplant in the first place, or it may be because their immune system is too immature to be able to suppress the expression of newly acquired food allergies.

Or it could be something about the liver itself, as there are cases that also describe people getting different organs from the same donor and only the person getting the liver developing a new food allergy. The liver contains blood stem cells that can develop into all types of blood cells, including immune system cells that could be sensitised to the donor’s trigger allergens.

Several risk factors for getting a food allergy after a liver transplant have been identified, including being younger than 2 years old, having a young donor, having asthma and/or eczema at the time of the transplant and contracting the Epstein–Barr virus.

Symptoms (often to multiple foods) generally manifest themselves within 18 months of the operation (with one single-centre study reporting that the risk of developing a food allergy within the first year is about 3 times higher than in subsequent years), although they can occur up to 17.6 years later.

Symptoms generally involve the skin; facial swelling (angio-oedema) and hives (urticaria) occur in around 4 to 5 in 10 people. Gastrointestinal manifestations (diarrhoea, vomiting, stomach pain) also affect around half of people with a liver transplant-acquired food allergy (LTAFA), while respiratory symptoms affect about 1 in 10. Anaphylaxis affects around 16 in 100 children with LTAFA, but no fatal cases have been reported so far. Although the majority (around 4 in 5) of the new food allergies are IgE-mediated, some people also get mixed or non-IgE-mediated allergies like Eosinophilic Gastrointestinal Disorders (EGIDs).

Although less common, there are also reports of people developing new allergies to egg after other types of transplant including several cases of bone marrow transplantations and cord blood transplantations which can lead to an eosinophilic gastrointestinal disorder. The latter type is more likely to resolve.

Most people who have a transplant-acquired food allergy don’t lose it. For example, this case involving a girl who had a liver transplant when she was 8 months old, subsequently developed allergies to sesame, milk, fish and egg, and was still unable to eat raw egg at the age of 11—although she could eat cooked eggs.

The early introduction of egg into the diet may help to prevent egg allergy.

There is a growing international consensus that the early introduction and regular consumption of allergenic foods, notably peanut and egg, may help to prevent IgE-mediated allergy to those foods, especially in infants considered at risk of developing food allergies (i.e. those with eczema, other food allergies, or family history of allergy).

As such, most guidelines advise introducing solid foods, including well-cooked forms of egg between the ages of 4 and 6 months, including those of:

• the European Academy of Allergy & Clinical Immunology (EAACI)
• the British Society for Allergy & Clinical Immunology (BSACI)
• the German Society for Allergology and Clinical Immunology (DGAKI)
• the American Academy of Paediatrics (AAP)
• the Canadian Paediatric Society (CPS)
• the Australasian Society of Clinical Immunology and Allergy (ASCIA)
• the Asia Pacific Association of Pediatric Allergy, Respirology & Immunology (APAPARI)

Several landmark trials provided the evidence to support these guidelines. The first was the British EAT (Enquiring About Tolerance) trial, that enrolled 1303 3-month old exclusively breast-fed infants between 2009 and 2012 and randomly assigned them to 2 groups which would either avoid or carry out an early introduction to six major food allergens—namely peanut, egg, milk, fish, sesame and wheat. The infants in the early introduction group were introduced to the foods at the age of 6 months and ate the equivalent of 4 g of cooked egg protein twice a week. All the infants were tested for food allergies between the ages of 1 and 3. The intervention was shown to be effective for both peanut and egg (and not the other foods). As far as egg allergy was concerned, 1.4% infants in the early introduction group who stuck to the protocol ended up developing an allergy to egg, versus 5.5% in the group who were not introduced to egg, representing a 75% lower risk.

A follow up study carried out in 2019 revealed that the early introduction of hard-boiled egg was also effective in high-risk infants (those sensitised to any food at enrolment and those with eczema of moderate severity), even if they did not strictly adhere to the protocol. Among those infants who were sensitised to egg at enrolment, 20% developed egg allergy compared to 48.6% of those who were not introduced to egg at an early age. Similarly, among those with moderate eczema at enrolment, 16.1% developed egg allergy compared to 43.3% of those in the standard introduction group. Equally importantly, the researchers noted that the early introduction of major food allergens into the diets of non–high-risk infants was not associated with an increased risk of developing food allergy.

In 2017, the results of the Japanese PETIT (Prevention of Egg Allergy with Tiny Amount Intake) trial were published, revealing similar results. The trial enrolled 147 4 to 5 month-old infants with eczema between 2012 and 2015 and randomly allocated them to 2 groups, which either carried out an early introduction of heated egg powder or took a placebo. The infants in the egg group ate 50 mg of heated egg powder every day between the age of 6 and 9 months, and then received 250 mg daily thereafter until they were 1 year old. Every effort was also taken to treat the infants’ eczema. Egg allergy was diagnosed in only 8% of the infants receiving the egg powder, and in 38% of the infants in the placebo group. Although the intervention was clearly effective, however, it did come with a higher risk of reactions.

Finally, the PreventADALL (Preventing Atopic Dermatitis and ALLergies in Children) study carried out in Norway and Sweden assigned a total of 2397 newborn infants to a skin intervention group, a food intervention group, a combined intervention group and a control (no intervention) group. In the food intervention group, infants were introduced to major food allergens at the age of 3 months. The risk of developing a food allergy by the age of 3 was shown to be reduced in the food intervention group compared with the no food intervention group, but not compared with the skin intervention group.

Other studies have provided corroborating results. In the Australian HealthNuts study, which included 2589 infants, those who started eating eggs after the age of 10–12 months were shown to be more at risk of developing egg allergy than those who introduced them earlier, between the ages of 4 to 6 months. This was the case for infants considered at a high risk of developing egg allergy (those with eczema, a history of reactions to other foods, or a family history of food allergy) as well as those considered low-risk.

A 2023 study from the US reported that egg allergy at the age of 2 was significantly higher in children who had delayed egg introduction compared with those who were introduced to egg during infancy (8% vs 1.4%, respectively). The advantage of early introduction to egg was still noticeable at the age of 12, with the risk of having egg allergy being higher in children whose introduction to egg was delayed (3.9%) versus those who had been introduced to egg during infancy (1.1%).

In 2025, Spanish researchers published the results of a study in which they investigated whether introducing baked eggs into the diet of infants aged between 4 and 6 months old could prevent against developing egg allergy. In this study, 27 infants were given oral challenges to baked egg and those who passed were randomly assigned into 2 groups, one in which the infants were given baked egg daily and one in which the infants continued to avoid baked egg. 6 months later, they were all given a challenge to boiled egg. The infants in the group who ate baked egg every day all passed their challenges, but less than half (47%) of those who had continued to avoid egg were able to eat boiled egg without reacting.

That is not to say that every study has produced evidence supporting the early introduction of egg as an effective method of preventing egg allergy. Several studies that have used pasteurised raw whole egg powder have not been so encouraging.

An Australian study, (also referred to as the Solids Timing for Allergy Research (STAR) trial) involving 86 high-risk infants with moderate to severe eczema reported that a third of the infants randomised to an early introduction group (from 4 months of age) developed egg allergy, compared with half of the infants put in the late egg introduction group (from 8 months of age). However, the numbers of children involved were too small to produce a statistically significant results because the study was stopped early due to a high frequency of allergic reactions, including anaphylaxis.

Another Australian study, the Beating Egg Allergy Trial (BEAT) reported that early introduction to egg reduced the proportion of high-risk infants sensitised to egg at 12 months; 11% of those eating egg powder from the age of 4 months compared with 20% of those avoiding egg during that time, but these results were not statistically significant.

A larger Australian trial involving 820 high-risk infants randomised to receive either raw egg or a placebo powder from the age of 4 to 6 months reported similar results in both groups; egg allergy developed in 7% of the infants receiving raw egg compared with 10.3% of the infants receiving the placebo powder. The researchers concluded that the regular intake of egg intake from age 4 to 6 months did not seem to substantially alter the risk of developing egg allergy by the age of 1, although they noted that the dose of egg (0.4 g egg protein per day) may not have been high enough.

In Germany, the Hen’s Egg Allergy Prevention (HEAP) trial involving 383 infants not sensitised to egg concluded that introducing egg in the form of pasteurised egg white powder into an infant’s diet between the ages of 4 and 6 months neither prevented sensitisation nor allergy to egg. What it did do was create a risk of allergic reactions in infants who were already allergic to egg at that age—thus a prevention strategy was already too late for them.

In sum, what the research done so far suggests is that, if you want to prevent your child from developing egg allergy, you need to:

• use a cooked form of egg
• feed your child around 2 g of egg protein twice a week (in total, the equivalent of a small hard-boiled egg)
• do not feed your child more than 4 g egg protein
• feed your child egg at least once a week, as irregular feeding is actually more likely to increase their chances of developing a food allergy

Finally, researchers have found evidence suggesting that early introduction might not be needed in populations where overall food allergy prevalence is low. The 2018 Growing Up in Singapore Towards healthy Outcomes (GUSTO) trial reported that food allergy rates in Singapore remained low despite the delayed introduction of allergenic foods. There was a trend between delayed introduction of egg (after the age of 10 months) and the development of egg allergy at 12, 18 and 24 months but this could have been due to random chance.

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